Major Sources of Commercially Viable Drugs
Naturally Occurring Drugs
are usually obtained from plant or animal sources.
1. Alkaloids: are nitrogen-containing compounds occurring in plants and possessing pharmacological activity. Most alkaloids have a basic character (e.g., morphine from opium poppy or atropine from belladonna), whereas others are neutral amides (e.g., colchicines from autumn crocus). All alkaloids end in the suffix –ine; however, not all drugs that end with this suffix are alkaloids (e.g., nifedipine [Procardia®] or meperidine [Demerol®]).
2. Hormones: are endogenous chemicals released into the blood by a tissue or organ to act on more distant tissues or organs. These may be biogenic amines, peptides/proteins, or steroids.
a. Biogenic amines such as epinephrine are released by the adrenal medulla to alter the function of multiple organ systems during sympathetic activation.
b. Steroids such as testosterone, estradiol, cortisol, etc. are chemical derivatives of cyclopentanoperhydrophenanthrene and often obtained from animal or human sources.
c. Peptides/proteins such as insulin, glucagon, and somatostatin are obtained from animal sources or recombinant DNA technology. Generally, peptide and protein drugs have limited oral activity and have to be administered parenterally.
3. Glycosides: are drugs that contain a sugar moiety bound to a nonsugar or aglycone portion via glycosidic bonds and are most often from plant (e.g., digoxin) or microbial (e.g., streptomycin, doxorubicin) sources.
4. Polysaccharides: are drugs composed of sugar polymers from human or animal sources (e.g., heparin, enoxaparin). Structural modification of naturally occurring sugars can yield additional drugs (e.g., sucralfate [Carafate®]).
5. Antibiotics: are often fungal or other microbial products that have suppressive or lethal effects on other microorganisms (e.g., penicillin, tetracycline).
6. Vitamins are plant and animal products that function as essential cofactors for various metabolic processes in the body. Water-soluble vitamins include thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), cyanocobalamin (B12), ascorbic acid (C), folic acid, pantothenic acid, and biotin (H). Fat-soluble vitamins include a-tocopherol (E), ergocalciferol (D), retinol (A), and phytonadione (K).
Synthetic products
1. Small organic molecules produced by organic synthesis to mimic the activity of naturally occurring chemicals or found to have unique pharmacological activity not previously identified.
a. Antimicrobials (e.g., ciprofloxacin [Cipro®] or trimethoprim) are man-made chemicals that inhibit unique microbial targets such as the DNA gyrase or dihydrofolate reductase to treat susceptible infections.
b. Receptor ligands compose the largest group of drugs and often mimic endogenous receptor ligands; for example, propranolol (Inderal®) has structural homology to epinephrine; meperidine (Demerol) mimics the structural features of endorphins at the m-opiate receptors.
c. Enzyme inhibitors may be targeted against microbial proteins as in section VIII.B.1.a above or mammalian enzymes; for example, aliskiren (Tekturna®) against renin, pravastatin (Pravachol ®) against hepatic HMG-CoA reductase, or imatinib (Gleevec®) against c-kit tyrosine kinase.
2. Peptides/proteins
a. Peptides. Eptifibatide (Integrilin®) is a synthetic cyclic peptide that mimics components of carpet viper venom to prevent platelet aggregation.
b. Proteins. Lepirudin (Refludan®) is a recombinant, synthetic derivate of hirudin, the anticoagulant from leeches.
3. Polysaccharides. The synthetic pentasaccharide fondaparinux (Arixtra®) mimics the portions of heparins that interact with coagulant proteins.
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